In mold-pressing machines of the kind referred to above, usually being adapted to operate automatically producing series of casting molds or casting-mold parts, it is of crucial importance that the correct quantity of liquid mist be injected in each cycle. Thus, an excess of liquid mist will, in addition to increasing the costs, create an unnecessary load on the environment, while too small quantities of liquid mist will result in an insufficient "lubrication" of the mold-chamber walls, in the worst case possibly causing the compacted object to stick to the mold-chamber walls, thus blocking the operation of the machine.
It is a relatively simple matter to ensure that the quantity of the injected liquid mist is held below a predetermined upper limit, this effect e.g. being attainable by means of a suitably time-controlled pump only applying pressure to the liquid to be atomized in a period corresponding to the desired quantity of liquid mist. Experience has shown, however, that it sometimes happens that the quantity of injected liquid mist is too small, and detailed investigations have shown that the cause is to be found in leaks--of shorter or longer duration--in the valve situated immediately upstream of the first nozzle aperture or the liquid-nozzle aperture in the atomizing nozzle concerned. Thus, such a leak will during the periods, in which the time-controlled pump mentioned does not apply pressure to the liquid-supply conduit, result in that the excess air pressure in the vortex chamber of the nozzle, due to the air pressure in the conduit concerned usually being maintained both before and after the periods in which there is a full pressure in the liquid-supply conduit, propagates backwards through the leaky valve to form an air pocket in the liquid-supply conduit. Then, when in the next cycle pressure is reapplied to the liquid-supply conduit for the spraying of a new portion of liquid mist, this air pocket will first have to be pressed out through the liquid-nozzle aperture, obviously shortening the interval during which the liquid is injected and hence reducing the quantity being injected.